100K megohm DC probe

Posted on Jul 19, 2012

A 741 op amp is used with 100% ac and dc feedback to provide a typical input impedance of 1011 ohm and unity gain. To avoid hum and rf pickup the input leads should be kept as short as possible and the circuit should be mounted in a small grounded case. Output leads may be long since the output impedance of the circuit is a fraction of an ohm

100K megohm DC probe
Click here to download the full size of the above Circuit.

With no input the output level is indeterminate. Including Rl in the circuit through lowers the input impedance to 22 M.

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